High-frequency vacuum tube circuit



July 9, 1946. H. c. LAwRENE, JR

HIGH FREQUENCY VACUUM TUBE CIRCUIT 2 Sheets-Sheet 1 Filed Oct. 28, '1945 ATTORNEY H. C. LAWRENCE, JR

HIGH FREQUENCY VACUUM TUBE CIRCUIT July 9, 1.946.

2 Sheets-Sheet 2 Filed Oct. 28, 1945 'TI/T12.

Patented July 9,Y 1946 .CIRCUIT Y e .I Howard C. Lawrence, Jr., Haddonield, NUI., as-l signor toRadioCorporation of America, fa cor-Y f poration 'of Delaware Y spp'iicaeonoctoberzs;1943, serial-N0. staats 'I'his invention relates toultra' highlfrequency 'oscillatorxcirculta .and particularly", to vacuum tube oscillatorsv generatin'goscillations higher` Ythan 300r megacyclesp; l;

:Among the objects ofthe present inventionr are To provide Aan yultra high frequency electron discharge device oscillator .having anode and cath-V 1; .odel'tuned circuitsV which are shielded fromreach other Yvili-thin the; device and `individually shielded externally of the device; toprovide a grounded grid-electron discharge device oscillator ofjoult'ra high frequencies Whose anodean'd cathodeelec-A trodeshave separate tunable circuits cou'pled'to.V

each other magnetically by means of a selective feed back loop; lto providev al grounded grid elec; Y

tron dischargeoscillator ofj ultra high frequencies whoseganode and jcathodeshave separate shielded-tunable circuits of distributed inductance and capacity extending .from oppositesides of the devicefbutcoupled together by means vof a selec- Y' tive feed back circuitproperly polarized to pro-l duce oscillations; to provide a grounded gridvelectron discharge device oscillator of yultra high fre-V quencies whose `cathodes and annales-each have` a shielded tunable circuitv of distributed constants and oi. a length Whichis a multiple of and greater thanonequarter of the length oi." the communication wave, these tunable anode and cathodeeir.-Y cui-ts vbeing coupled togetherby a tunable selective feed back circuit*l v A more detaileddescriptionof the invention follows inl conjunctionvfwith drawings, wherein:

' `Figure 1 shows a circuit diagram., partly schematic and partly mechanical -ofr-the' ultra high frequency oscillation generator of` the invention; Figure 2 shows the essential details of themechanical construction yofthe oscillation vgenerator of Figure 1; and f Figure 3 is asection along line 3--3 of Figure 2. Referring, to Figure 1 in more detail, there is shown anoultr'a high frequency generator comprising a pair of vacuum tubes I and I I mounted in andsupporte'd Iby va metallic `plate I2. This metallicplate is provided Vwithv a pair of apertures I3, -I3 ioraccommodating the envelopes of the vacuum tubes.Y The grids ofthe tubes i0 and -Ii v j are directlygconnectedto the metallic plate I2,

Whichin turn is grounded.. [It'will thus besseen that the grid of each tube and associated mounting electrostatically shields the anode and cathode and their associated circuits from each other. A tunable' parallel conductor circuit composed of. hollow conductors I4 connect the anodes of the two tubes ktogether in push-pull relation. The ends of conductors I4 `at I5 are.. in telescopic relation to the otherY portions of the conductors in order Yto provide adjustment of the lengths `of these con- Putting, it in other ductors for tuning purposes. words,.w e have essentially a collapsible end I5 for tuning the anode circuit. Another pair of holl low= conductors,y I5 lforms ai tunable circuit between the cathodes oithe tubes. The conductors. IVG-.are

directlyconnectedftogether by- ,meansiof a short circuitingdisc Il forming ther bottompartv of 'an operinietallic.can-likearrangementJ.` The fila-. v

` ments V.Oithe twoltubeslil and fI I 'are supplied with heating currents through .Wires extending Within the interiors ofthe hollowy conductors I6 and connected Vto-the secondary Winding .of aV suitablefilament supply `transformer I9 whose prima-ry'winding is connected to .a-flow frequency v alternating current filament heatingi,. sojurce.

The anodes of` the two tubes Iiiand I Iv are supplied vvith ga, suitable positiver polarizing. potential from conductor. 2!)` which is. connected to. the up,-

per eadjrtcent` ends of the conductors I4 ofthe anode tuned circuit. The cathode tuning circuit is tunable bymoving the can I 8 upor down along the lengths of the conductors I5 by meansof asl-litable` rod` connected to pla-te: I1. Thefanode and cathode tuned'rcireuits I4 A and I 6,4v respectively .are

separately shielded by lu nllovvmetallic-semi-cirF cular sheets represented diagrammatically inuligure 1 by means of the dash-lines? I. It willvzthus p be seen that the anode and cathode tuned circuits are shieldedirom eachy other externallyv ofthe vacuumtubesllaand IfI by sheets 2| 'and also shielded f from each other electrostatic/ally' ...by means ofthe grounded gridsu which are directly connectedtothe metallic disc-,like plate- I2. The can I8, it should be noted, .is `open at the end `.nearf est the'cathodes.v Can I8` isy separatedby` anair gap fromthe shield 2l andA is. capacitively coupled totheshield. ..7-

In order to provide feed-back between the anode and cathodecircuits, thereis provideda selective; feed-backcircuit in the form oflan S-shaped conductor comprising loops r3i] 'and.3I. It will be seen. that loop 39,;is above the metallic plate I2 While. the loop 3l .isrbelow the. metallic platev I2, bothA ofthese loops fbeingconnected-.together .through an aperture 32 in the plate I2. The vmidpoint of the feed-back conductor is connected to the central conductor of a concentric line 33. The inner and outer conductorsof this concentric line33 arel adjustable in length by means Vof a slider 34.v The elective length of coaxial line v33 measuredvbetween slider 34 and the .midpoint of thevselective feedbackcircuit 39,31 is more than one-quarter of a wavelength at the operating frequencytandvhence acts as a capacity reactance for certain frequencies of operation; f. The total length of the loops SIland 3! is physically less than one-half wavelength; but by means of the tunable'I capacity reactance constituted by the coaxial line 33,4 the capacitance of this line tunes the feed back circuitto onehalf wavelength. While the effective lengthoi linev 33 -ismentioned as beingsuch that-,it is capacitative at certain frequencies of operation,

3 it should be understood that it maybe capacitive or inductive depending upon what is needed to tune the feed back loop. This would mean that the stub may be of a length up to one-half wavelength instead of the mentioned above. The longer than one-half wavelength but an inductive reactance to be electrically one-half wavelength at the operating frequency. The loops 30 and 3I are made in the form of an S in order to assure the fact that the voltage fed back to the cathode circuit is 180 -out-of-phase relative to the alternating current cathode potential. These oppositeV halves of the feed back conductor are 180 out-of-phase insofar as the magnetic field is concerned. The distance between the metallic plate I2 and each of the short circuiting conductors I5 and I'I of the anode and cathode tuned circuits is electrically three-quarters of a wavelength at the operating frequency.

The output circuit includes a metallic loop 24 which is arranged above the plate I2 for coupling to the anode tuned circuit. One end of the output loop 24 is connected directly to the plate I2 while the other end extends down through an aperture 35 for connection to the inner conductor of a concentric transmission line 38. Concentric transmission line 36, which connects the output loop 24to a suitable utilization circuit such' as an antenna, is shown provided with impedance matching stubs 31, 3T spaced one-quarter of a wavelength apart. A cathode bias resistor 40 is connected between ground and that end of the cathode conductor I6 farthest removed from the vacuum tubes. In the operation of the system of Figure l, the metallic can I8 for tuning the cathode tuned circuit serves as one terminal of acondenser whose other terminal comprises 'the grounded metallic shield 2l.

The lengths of the anode and cathode tuned circuits, which are here shown to be electrically (although not necessarily mechanically) threequarters of a wavelength long. enable the attendant to tune the circuits at the extremely high frequencies at which the oscillator is capable of functioning. The use of multiple quarter wavelength lines isy made possible by the selective feature of the feed back circuit. The selective feed back circuit comprising the loops 30 and 3I in the form of an S is tuned to the desired oscillation frequency by means of the variable capacitive reactance comprising the tunable coaxial line 33, thus controlling the frequency at which the oscillator functions. Putting it in other words, oscillations occur at the frequency of the feedback circuit only.

The oscillator of Figure 1 can be operated anywhere in the range from 350 to 1400 megacycles with anode voltages supplied to lead 20 anywhere in the range from 300 volts to 15,000 volts. Obviously,A if the circuit of Figure 1 is to be operated continuously, the anode voltages would be somewhere near the 300 volt figure, whereas if the oscillation generator of Figure 1 is to be used for pulse operation, for extremely short intervals of the order of a miscrosecond or so, the anode voltage may be in the upper regions near 15,000 volts. By means of the arrangement of Figure l, it is possible when using pulsing methods to obtain an output of at least 350 kilowatts employing an anode voltage of around 15,000 volts. Such pulse operation is obtainable by interrupting the anode voltage supply at the rate at which itis desired to produce pulses of high frequency energy.

one-quarter wavelength feed back loop may be -f tuned by` Vupper halves of the anode Figure 2 shows a mechanical construction of the'ultra high frequency oscillation generator of Figure `1. The oscillator is shown with the two circuit shielding systern separated and with one-half Yof the lower cathode circuit shielding system missing, to simplify the drawings. The metallic plate I2 shown in more detail in Figure 3 is hidden by means of the roundedmetallic sheet 50; Sheet 50 is provided with upper and lower shoulders 5I for accommodating and supporting the semi-cylindricalshields 2I1,;2I The shields for the anode and, cathode tuned circuits each comprise two halves which 'are screwed together at the apertures 52. One-half of the shield for the anode and 'thecathode tuned circuitslis shown connected to the'metallic sheet' 50. The otherfhalf of the shield 2| forthe cathode tuned circuitis provided in the complete assemblage'but is not shown in order not to complicate Vthe drawings. It should be understood at this time that the parallel transmission line circuit comprising the anode conductors I4 is across between a *concentric* line and a parallel conductor circuit by virtue of' the fact that the metallic 'casey'2vI, v2l 'enclosing this line is an essential part ofthe anode circuit and is not merely a shield. The coaxial line 33 for tuning the selective feedback circuit is shown the position of the. can I8 in tuning the cathodev circuit. The bottom ends'f the conductor IE of the cathode tuned circuit are connected together by means of a'metallic' plate 55 mounted in turn upon an insulator board 56. It should be noted that the plate 55 to which the cathode conductors I6 are connected is not connected to the shield 2|. 1t should also be noted that the can I8 is separated by an air'space from'the shield 2|. v The top of vthe' shield 2I for-*the anode tuned circuit 'is open to enable the circulation of cooling fluid. This cooling fluid in the form of air from a suitableblower is supplied to the interior ofthe shieldsZI both 'above and below the metallic dividing plate I2 by means of a rubber conduit 51 and air vents 58.

The conductors of the anode tunedl circuitare connected to the anodes-,of the vacuum tubes I0 and II by means of metallic flanges (il).v That portion of each of the conductors I4 of the anode circuit which is nearest the anode of the tubes is cut away and provided withV a metallic meshlike sieve 6IY for enabling air to flow freely therethrough.

The preferred type of vacuum tube to be used in the invention is one having an anode provided with a multiplicityk of anode fins for cooling purposes. It is important that the grid ofthe tube do av good shielding jobb'etween the' cathode and anode. One such tube which has been used is the RCA A-2212 tube shown-,very generally 'in Figure 3, which is a cross section of VFigure 2 along the line 3 3; The anode'fins are shown as horizontal metallic rings 62.` The grid, anode and cathode electrodes are arranged concentrically Within the tube envelope. The grid extends downward and is connected by means of a metallic flange 63 to'the plate I2. ,The cathode extends below -th'e flange 63 and is vconnected'to the conductor I6 of the cathode tuned circuit. Although the anodens of the vacuum tube have been shown to be horizontal, it Ashould be underamarres nectingv said anodes together, a parallel .conductor tuned circuit 'of substantially distributed constants connecting said cathodes together, a metallic shield connecting said grids together, a connection from ,said shieldy to ground, means external of saidtubes for shielding said tuned circuitsfrom each other, and a selective feedback circuit coupling said two tuned circuits, said'feedback circuit including a variable reactance for tuning said feedback circuit, said variable reactance comprising an adjustable coaxial line whose eiective length is less than one-half `wavelength at the operating frequency.

ll. An ultra high frequency oscillator comprisingapair of vacuum tubes each having .an anode, 'a .cathode and a grid, a tuned circuit of substantially. .distributed constants connecting said anodes together, a vtuned circuit of substantially distributed constants connecting said cathodes together, means electrostatically shielding the anode and cathode of each tube from each other, means external f said tubes for shielding said tuned circuits from each other, and a selective feedback circuit'coupling said two tuned circuits, saidv feedback circuit including an S-shaped conductor oppositehalves of which are 180 out-ofphase for the magnetic field and a variable capacitive reactance connected to the' midpoint of said S-shaped conductor for tuning the selective circuit to the frequency at which said oscillator should function. E l2. An ultra high frequency oscillator comprising a pair of vacuum tubes each having. an anode, a cathode and a grid, a parallel conductor tuned circuit of substantially distributed constants connecting said anodes together, a parallel conductor tuned circuit of substantially distributed constants connecting said cathodes together, means electrostatically shielding the anode and cathode of each tube from each other, means external of .said tubes for shielding said tuned circuits from each other, and a selective feedback clrcuitcoupling said two tuned circuits, said feedback circuit including an Sl-shaped conductor opposite halves of whichA are 180 out-of-phase for the magnetic field and a variable reactance connected to the midpoint of said S-shaped conductor for tuning the selective circuit tothe frequency at which said oscillator should function, said reactance comprising an adjustable coaxial line whose effective length is less than one-half wavelength at the operating frequency.` v 13. An ultra high frequency oscillator comprising a vacuum tube having a cathode, an anode and a grid, individual tunable resonant circuits for said cathode and anode, means external of said tube for shielding said resonant circuits from each other, a direct conductive connection from said shield to said grid, a feedback loop magnetically coupling vsaid tuned circuits together, and a variable capacitive reactance for tuning said loop to the frequency of operation of said oscillator. v

' 14. An ultra high frequency oscillator comprising a pair of vacuum tubes each having an anode, a cathode and a grid, a parallel conductor tuned circuit of substantially distributed constants connecting said anodes together, a parallel conductor tuned circuit of substantially distributed constants-connecting said cathodes together, means electrostatically shielding the`anode and cath- `ode, of each tube from each other, means external of saidtbes for shieldingsaid tuned circuits from each other, and a selective feedback circuit couplingsaid two tuned circuits,y said feedback circuit including a variable capacitive `-reactance for tuning said` feedbackA circuit, said variable capacitive-reactance being composed offan-ad justable. coaxial Yline whose effective length vis more than one-quarter wavelength at the 'operating frequency.

15. An ultrahighfrequency oscillator comprising a pair of vacuum tubes eachfhaving an anode, a cathode and a grid,"a tuned'circuit of substan tially distributed constants4 connecting said anodes together, a tuned vcircuit of substantially distributed -constants .connecting saidcathodes together, means electrostatically shielding the anode and cathode of each tube fromeach other, means external of said tubesv for shieldingA said tuned circuits from eachother, and a selective feedback circuit coupling said two tuned circuits, said feedback circuit including a variable reactance for tuning said feedback circuit, said variable reactance comprising an adjustable 'coaxial line whose effective length is less than one-half Wavelength at the operating frequency.

16. A radio frequency Voscillatorcomprising a vacuum tube having a cathode, an anode and a grid, individual tuned resonant circuits for said anode and cathode located on' opposite sides of said rtube, a shield intermediate said tuned lcircuits and connected to said grid, said shield having an aperture, and a selective feed back extending through said aperture and comprising ari'S'- shaped conductor whose oppositeY halves are on opposite sides of said shield. Y

1 7. An ultra high frequency oscillator comprising a pair of vacuum tubes each having an anode, a cathode and a grid, a tuned circuit of substantially distributed constants connecting said anodes together, a tuned circuit of substantially distributed constants connecting said cathodes together, a metallic shield directly connectingl said grids together, a direct connection from said shield to ground, means external'of Asaid tubes for shielding said tune'd circuits from each other, and a selective feed back circuit coupling said two tuned circuits, said feed back circuit including a' variable reactance for tuning the same to the frequency at which said oscillator should function.

18. An ultra high frequency oscillator comprising avacuum` tube having a cathode,` an anoder and a grid,..individual'tunable resonant circuitsfor said cathode and anode, means 'external of said tube' for shielding said resonant circuits from: each other, a direct conductive connection from said shield to said grid, a tunable feedback loop magnetically coupling said tuned circuits together, and an adjustable'stub tuner connected to the center of said loop.

19. An ultra high frequency oscillator comprising a vacuum tube having a cathode, an anode and aV grid, individual tunable resonant circuits for said cathode and anode, meansexternal of said tube for shielding said resonantcircuits from each other, a direct conductivev connection from said shield to said grid, afeedback loop magnetically coupling said tuned circuits together, and a reactance circuit coupling the center of said loop to said shield.v

HOWARD C. LAWRENCE, Jn 

